Generally, a transparent conductive film must have high conductivity (surface resistance of 1×103 Ω/sq or less) and high transmissivity in a visible region. Such a transparent conductive film is used to manufacture plasma display panels (PDPs), liquid crystal displays (LCDs), light emitting diodes (LEDs), organic light emitting displays (OLEDs), touch panels, solar cells, and the like.
Particularly, in the present invention, a transparent conductive film used to manufacture a touch panel will be described.
Generally, a touch panel is an apparatus for recognizing input signals generated by touching letters or figures displayed on a liquid crystal display screen with hands or touch pens without using additional input devices, such as keyboards, mousse, and the like.
Such a touch panel, as shown in FIG. 1A, includes: a liquid crystal display (LCD) screen 10; a protective layer 20 formed on the liquid crystal display (LCD) screen 10 to protect the liquid crystal display (LCD) screen 10; a transparent conductive film formed on the protective layer 20, the transparent conductive film including a lower transparent electrode 30, an upper transparent electrode 40, and a spacer 50 interposed therebetween; and an external protective layer 60 made of polymethylmethacrylate (PMMA), the external protective layer being formed by a hard coating method.
The protective layer 20 for protecting the liquid crystal display screen 10 is generally made of polycarbonate, and the lower transparent electrode 30 and upper transparent electrode 40, which constitute a transparent conductive film, must function as electrodes and simultaneously have a transmissivity of 70% or more in a visible region.
Conventionally, an indium tin oxide (hereinafter, referred to as ‘ITO’) electrode is most widely used to manufacture the transparent electrode. The ITO is advantageous in that it has excellent physical properties and has been frequently used in a process of manufacturing a transparent electrode to date, but is problematic in that, since indium oxide (In2O3) is obtainable from a zinc (Zn) mine just as a by-product, the supply and demand thereof is unstable. Further, ITO film is problematic in that since the ITO film does not have flexibility, it cannot be used for flexible products, and further in that since the ITO film is manufactured under high temperature and high pressure conditions, the production cost thereof is increased.
Further, when the protective layer formed on the liquid crystal display is coated with the ITO in order to be used as the transparent electrode of the touch panel, the most important problem is the adhesion between the ITO and the polycarbonate constituting the protective layer. Generally, since the adhesion between the ITO and polycarbonate is not high, a polyethylene terephthalate (PET) substrate is coated with ITO, and then adhered on the protective layer made of polycarbonate.
However, this method is problematic in that the transmissivity of the liquid crystal display screen is decreased, and in that a process of coating a polyethylene terephthalate (PET) substrate with ITO is additionally conducted, so that costs are increased, thereby increasing the thickness of the touch panel.